The present invention relates to a serial memory which has, for example, a function of serial input/output of data for image systems and more specifically to a technique suitably applied to image processing systems and other systems that process print data in a bit map format.
There is generally known a serial memory, which internally converts serial input data into parallel data and writes the data into a memory array two or more bits at a time, and which internally converts data that was read two or more bits at a time from the memory array into serial data and puts out the converted data in the same order that the data was input. A prior application filed by this inventor (Japanese Patent Application No. 108503/1991) discloses a two-dimensional compatible serial memory, which incorporates a line increment function that allows quick access from an arbitrary point to the beginning of the next line, and which further includes a window scan mode whereby a horizontal address (a resetting destination during the execution of the line increment) can be set and fixed from "0" during the normal mode to any arbitrary address, making it possible to scan a rectangular area cut out from any part of the screen. In a separate application filed by this inventor (Japanese Patent Application No. 181738/1992), another type of serial memory, though not generally known, is disclosed which has a jump function that allows a serial access to start from an arbitrary address and a line increment function that permits quick access from any point on the two-dimensional screen to the beginning of the next line.
There are no large-capacity serial memories available, however, which provide a practical means for outputting the entire or any part of input data in an order reverse to that in which the data was input, and which realize this output mode by means of a mode switching or selection. Nor are there any examples of application of such memories to systems. Under these situations, when a need arises to reverse the order of scanning in image processing systems, it is necessary either to add a line memory having a last-in-first-out (LIFO) function to the system to reverse the order in which parts of serial memory data are output, or to operate the hardware of the system in reverse order.